1. Field of the Invention
The present invention relates to a laser processing method for marking, or performing similar processing on, a surface of a processing target by radiating a laser beam on the processing target, and a semiconductor device obtained by using the processing method.
2. Description of the Related Art
As examples of a conventional marking method using a laser beam, the following laser processing methods have been known.
Description will be given of how, for example, an English letter “A” is marked as shown in FIG. 6A. An information converting unit of a marking machine performs arithmetic on various data inputted into a marking information input unit, and converts the data into marking data. Specifically, marking data (surface data), which is denoted by reference numeral 41, is converted into multiple small pieces of horizontal data (scanning data in a lateral direction of the drawing) as denoted by reference numeral 42.
FIG. 6B shows some pieces of the horizontal data (scanning data in the lateral direction of the drawing). Each of the pieces of the horizontal data (scanning data in the lateral direction of the drawing), which are denoted by reference numerals 43 to 46, indicates that, for example, a laser beam should be turned off in white regions and turned on in black regions. In addition, the marking machine controls a laser beam source unit and so forth, and hence performs laser processing based on all the pieces of the horizontal data (scanning data in the lateral direction of the drawing) from an uppermost portion of FIG. 6A to a lowermost portion thereof. Thus, the English letter “A” is marked on the surface of the processing target. This technology is described, for instance, in Japanese Patent Application Publication No. Hei 5-162441 (pages 2-3, FIGS. 1 and 3).
Moreover, there is a known method for marking, by using a laser, a surface of a package made of a plastic, ceramic, resin or the like, and including semiconductor integrated circuits. This technology is described, for instance, in Japanese Patent Application Publication No. Hei 9-220686 (pages 2-4, FIGS. 1 and 7).
As described above, in the conventional laser processing methods, for example, the English letter “A” is marked by combining multiple pieces of the horizontal data (scanning data in the lateral direction of the drawing). Accordingly, the number of pieces of the horizontal data is large. Particularly, marked letters and the like such as marked English letters and marked figures are usually designed vertically long. For this reason, the conventional laser processing methods inevitably handle a large number of pieces of horizontal data, as well as bring about a problem of difficulty in shortening time needed for the marking, and a problem of poor workability of laser marking.
In addition, the conventional laser processing is performed from a left end portion toward a right end portion of each of pieces of horizontal data (scanning data in the lateral direction of the drawing). After a laser processing is ended based on one piece of the horizontal data, another laser processing is similarly performed on the next piece of the horizontal data positioned below from a left end portion toward a right end portion thereof. In other words, in the conventional laser processing methods, the laser beam source unit moves a long distance during a non-marking period between each two adjacent pieces of the horizontal data. Such a laser processing method also has the problem of difficulty in shortening time needed for the marking.
Moreover, as shown in FIG. 6B, each of the pieces of the horizontal data (scanning data in the lateral direction of the drawing), which are denoted by reference numerals 43 to 46, indicates that a laser beam should be turned on in the black regions and turned off in the white regions. As illustrated, in an “inverted V” portion of the English letter “A,” most of each piece of the horizontal data represents the white regions, implying that the non-marking period is long. Such a laser processing method also has the problem of difficulty in shortening time needed for the marking.
FIG. 6C shows how a laser processing is performed on a region indicated by a circle 47 in FIG. 6A. As described above, the English letter “A” is marked by the combination of the laser processings based on the multiple pieces of the horizontal data (scanning data in the lateral direction of the drawing). Accordingly, in the “inverted V” portion of the English letter “A,” as shown in FIG. 6B, the starting position of the laser processing is shifted outwardly stepwise. Thus, the English letter “A” is laser-processed in a way that the border of the letter A is shaped like steps. The English letter “A” not having a smoothly-shaped border brings about a problem of poor visibility. Further, when the marked letter or the like is used for pattern recognition, the border shape may deteriorate the letter recognition accuracy in some cases. Particularly, when the border of a letter to be marked has a curved line, there is a problem that it is difficult to form the curved line in a smooth shape.
Packages including semiconductor integrated circuits are mounted in portable electronic devices such as cellular phones or digital cameras. Recently, as the portable electronic devices and the like become thinner, the very packages to be mounted there are demanded to be thinner. Accordingly, there is no room left in the thickness of such packages. If the package surfaces are laser-processed too deeply, a problem occurs in which thin metal wires may be exposed to the outside from the marked area or may be seen through the package surfaces, and consequently the packages are treated as defective products.
Furthermore, since a company logo, product number and the like are marked on the package surface, letters and the like to be marked are designed using several line widths. Thus, a unicursal approach using a laser beam of one fixed width does not enable the aforementioned company logo, product number or the like to be marked by a single laser processing. For this reason, the laser processing has to be performed several times to mark the aforementioned company logo, product number and the like. In this event, if laser processing lines intersect each other, the package surface is processed too deeply in the intersection region, resulting in the aforementioned problem of a package defect.